5 Reproduction, Dispersal, and
Migration
Notes for Marine Biology:
Function, Biodiversity, Ecology
By Jeffrey S. Levinton
©Jeffrey S. Levinton 2001
Sex and Reproduction
• IS SEX NECESSARY?
• WE MUST SEPARATE SEX AND
REPRODUCTION?
• SPECIES CAN REPRODUCE
WITHOUT SEX (CLONAL GROWTH
INVOLVING FISSION OR BUDDING
OF INDIVIDUALS)
Sex and Reproduction
• Non-sexual reproduction:
Descendants are genetically identical
- clone
Colonial species produce a set of
individuals that are genetically
identical, known as a module; each
module may have arisen from a
sexually formed zygote
Cost of Sex
• FEMALE gives up half her possible
genes in progeny
• Sex involves expenditure of energy
and time to find mates, combat
among males
Benefits of Sex?
• genetic diversity - sex increases combinations of
genes - resistance against disease
• Alternative to sex: clones, must wait for
mutations to occur
• Sex - recombination produces variable gene
combinations, meiosis enhances crossing over of
chromosomes: new gene combinations and
intragenic variants
Sexual Selection
• selection for extreme forms that breed
more successfully - major claw of fiddler
crabs, deer antlers, colors of male birds
• Can involve selection for display
coloration, enhanced combat structures
• Female choice often involved; selection
for fit males (good genes hypothesis)
Sexual Selection
The major claw of fiddler crabs is employed
for display to attract females and for combat
with other males
Types of Sexuality
• Separate sexes -gonochoristic
• Hermaphroditism -individual can have
male or female function
Hermaphroditism
• Simultaneous
• Sequential
Protandrous - first
male,then female
Protogynous - first
female then male
Sequential Hermaphroditism
• Protandry - size advantage model
• Eggs costly in terms of resources, so more offspring
produced when individual functions as female when large
• Male function does not produce great increases in
offspring when it gets larger
Therefore, there is a threshold size when female function
begets more offspring.Smaller individuals do better as
males.
Number of offspring produced
Male at advantage
Female at advantage
Female
Male
Body size
The size advantage model for Protrandry
Protogyny
• Male function must result in more
offspring when male is older and larger
• Important when aggression is important
in mating success, e.g., some fishes where
males fight to maintain group of female
mates
Male polymorphism
• Males may occur as aggressive fighting morphs, or less
aggressive morphs
• Found in a number of groups, e.g., some fishes and some
amphipod or isopod crustaceans
• Determination of morphs can be environmental, genetic
• Less aggressive morphs can obtain mates by “sneaky”
tactics, which are often successful
Factors in Reproductive Success
• Percent investment in reproduction reproductive effort
• Age of first reproduction (generation
time)
• Predictability of reproductive success
• Juvenile versus adult mortality rate
Life History Theory
• Tactics that maximize population growth
• Evolutionary “tactics”:Variation in
reproductive effort, age of reproduction,
whether to reproduce more than once
• Presume that earlier investment in
reproduction reduces resources available
to invest in later growth and survival
Examples of Life History Tactics
• Strong variability in success of
reproduction:reproduce more than once
• High adult mortality: earlier age of first
reproduction,perhaps reproduce only
once
• Low adult mortality: later age of first
reproduction, reproduce more than once
Example: Selection in a Fishery
• Shrimp Pandalus jordani,protandrous
• Danish, Swedish catch (Skagerak)
1930-1956 – stable, increased slowly
1956- 1960 – catch tripled (2000  6300
ton/y)
Pandalus jordani fishery
Changes in Body Size
Period
1949-1950
1954-1957
1961-1962
% over 80 mm Somatic
growth
change
44%
0
25%
0
14%
0
Changes in Size of Change from Male to Female
Period
Before 1954
1954
1955-1962
% females < 75 mm
long
0
7% (65-74 mm)
14 % (55-74 mm)
Sex - factors in fertilization
• Planktonic sperm: (and eggs in many
cases). Problem of timing, specificity.
• Direct sperm transfer:
(spermatophores, copulation).
Problem of finding mates (e.g.,
barnacles, timing of reproductive
cycle)
Planktonic sperm and eggs
• Specialized binding/fertilization proteins
in sperm and receptors in eggs (bindin in
sea urchin sperm, lysin in abalone sperm)
• Sperm attractors in eggs
• Binding proteins are species-specific,
proteins with high rates of evolution
Gamete matching important in
plankton
Timing of sperm and egg
release
• Epidemic spawning - known in mussels,
stimulus of one spawner causes other
individuals to shed gametes
• Mass spawning - known in coral species, many
species spawn on single nights
• Timing of spawning (also production of spores
by seaweeds) at times of quiet water (slack high
or low tide) to maximize fertilization rates
Movement of Marine Organisms
Dispersal versus migration
DISPERSAL: UNDIRECTED
MIGRATION: DIRECTED, RETURN SPECIFIC
Migration scheme
Adult Stock
Spawning
Area
Nursery/Juvenile
Feeding Area
Migration Types
• ANADROMOUS - fish live as adults in salt water,
spawn in fresh water (shad, striped bass), more
common in higher latitudes
• CATADROMOUS - fish live as adults in fresh water,
spawn in salt water (eel) more common in lower
latitudes
• FULLY OCEANIC - herring, green turtle
Migration
Geographic Specificity of
migration - non-specific in
some, very specific in others
(green turtle, oceanic salmon)
Norway
Migration of
the herring
in the North
Sea
Adult
feeding
area
Spawning
areas
EEL MIGRATION - adults live in marshes, creeks
(European – Anguilla anguilla, American – Anguilla
rostrata), migrate to Sargasso Sea, spawn, die, juveniles
drift in currents and American eels swim to shore,
European eels drift across Atlantic
N. America
Europe
Africa
Larval Dispersal
Dispersal Types in Benthic
Species
• PLANKTOTROPHIC DISPERSAL - female produces
many (103 - 106) small eggs, larvae feed on plankton,
long dispersal time (weeks), some are very long
distance (teleplanic) larvae - cross oceans
• LECITHOTROPHIC LARVAE - female produces
fewer eggs (102 - 103), larger, larvae live on yolk, short
dispersal time (hrs-days usually)
• DIRECT RELEASE - female lays eggs, or broods
young, juveniles released and crawl away
Lecithotrophic larva: tadpole larva of the
colonial ascidian Botryllus schlosseri
Planktotrophic larva of
snail Cymatium parthenopetum
Pluteus larva of an urchin
PROBLEM OF SWIMMING LARVAE:
water motion carries them away from
appropriate habitats
Loss to offshore waters
Wind-driven
recruitment
onshore
Self-seeding
eddies
Longshore drift
Shore Population
Internal waves,
tidal bores
Some helping hands in dispersal
• Winds that wash larvae to shore
• Internal waves - bring material and
larvae to shore
• Eddies that concentrate larvae in spots
• Behavior - in estuaries can allow
retention (rise on the flood tide, descend
on the ebb tide)
Estuarine larval adaptations - retention
Larvae rise on the flooding tide, sink to bottom on the
ebbing tide: results in retention of larvae within estuary
Estuarine larval adaptations - movement of
larvae to coastal waters, return of later stage
larvae
Blue crab, Callinectes sapidus
Recruitment of juvenile corals
Effect of local eddies on larval retention in a
patch reef on the Great Barrier Reef,
Australia
Planula
larva
Distance from reef perimeter
Newly settled coral
Why disperse?
• High probability of local extinction; best
to export juveniles
• Spread your young (siblings) over a
variety of habitats; evens out the
probability of mortality
• Maybe it has nothing to do with dispersal
at all; just a feeding ground in the
plankton for larvae
Settling problems of planktonic
larvae
• Presettling problems:
Starvation
Predation in plankton
Loss to inappropriate habitats
Example of Effect of Starvation:
Phytoplankton variation and barnacle larval success
Abundant diatoms
Number of larvae
1000
500
1950
Normal
phytoplankton
Early
Larval
stages
Later
Larval
Stages
0
1951
Failure of
phytoplankton
Diatom
1000
failure
500
0
March
April
Semibalanus balanoides settlement in a Scottish Sea Loch
Postsettling problems
Expectation of life
(months)
• Energetic cost of metamorphosis
• Predation
• Crowding --> mortality
Initial
6 months
12 months
18 months
Interindividual contacts per cm 2
Expectation of life of Semibalanus balanoides as function of crowding
Free-swimming larva
Selection
Behavior
Alternating
Releasor
Random contact Photo+ and
Photo- stages
With a
surface
Releasor
Selection behaviorcrawling and test
surfaces
Releasor
Releasor
Contact w. Contact w. Contact w.
Substance on
pits and Sfc. Of another adults of
grooves
same sp.
species
Block in
behavior,
contact with
inappropriate
surface
Block in
behavior,
e.g., contact with
crowded surfaces
Selection behaviorfrequent turning
and flexing
ATTACHMENT
Stages in the selection of substratum by planktonic larvae
The End